LeetCode 3 - Longest Substring Without Repeating Characters - 2022.12

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        """ How to solve it: we're going to move a sliding window through the input,
        maintaining a dictionary of the characters in the current window, as well as a
        variable tracking how many of the entries in the dict have more than one
        character.  We'll update a variable tracking the length of the longest substring
        whenever the dict doesn't have any characters with more than one entry in the
        current window.  We'll advance the right pointer as long as the current window
        doesn't have any duplicates, and we'll advance the left pointer as long as the
        current window *does* have duplicates.
        """
        longest_substring = 0
        l = 0
        r = 0
        current_window_dict = defaultdict(int)
        chars_in_dict_with_dupes = 0

        def we_could_still_find_a_substring():
            return l <= r and r < len(s)

        while we_could_still_find_a_substring():
            while chars_in_dict_with_dupes == 0 and r < len(s):
                longest_substring = max(longest_substring, r - l)
                current_window_dict[s[r]] += 1
                if current_window_dict[s[r]] == 2:
                    chars_in_dict_with_dupes += 1
                r += 1

            while chars_in_dict_with_dupes > 0 and l <= r:
                current_window_dict[s[l]] -= 1
                if current_window_dict[s[l]] == 1:
                    chars_in_dict_with_dupes -= 1
                l += 1

        if chars_in_dict_with_dupes == 0:
            longest_substring = max(longest_substring, r - l)


        return longest_substring